Having met the chilling requirements of endodormancy, the cold-heat interaction effect appears, and the ecodormancy stage has begun. During ecodormancy, the buds gradually acquire the ability to sprout. The chill needs of both stages are complementary and their addition is the entire requirement of latency. To study the chilling requirement of endodormancy it measured the effects that produce growing quantities of chill unit Utah modified (CU) and small amounts of growing degree hours (GDHºC) on the vegetative budbreak of Brooks, New Star, Garnet and Stella varieties. The tests were performed on materials that receive UFUM under controlled and field conditions and GDHºC under field and greenhouse condition. The models conveniently estimated the behavior of budbreak. The endodormancy requirements were 355, 530, 469 and 736 and the ecodormancy requirements were 460, 480, 370 and 560 respectively for Brooks, New Star Garnet and Stella varieties. Due to cold-heat interaction at ecodormancy stage, the requirements vary with both the variety and availability of winter chill and spring heat. During the ecodormancy, when only the heat is increased, usually achieved greater budbreak response than those in which only the cold increases (Brooks, New Star and Stella). Other variety like Garnet the effect of cold-heat is more balanced. Among these varieties endodormancy requirements have greater variability than those of the ecodormancy.